Experimental murine salmonellosis is accepted as an animal model for human infection with Salmonella typhi, which causes significant worldwide illness. As a result there is continued interest in elucidating the mechanisms of pathogenesis and immunity of Salmonella enteric fevers in order to develop more effective, less toxic vaccines. With respect to vaccine development it is important to note that Salmonella has become an important opportunistic infection in patients with AIDS. The work proposed here intends to examine the role of T cells in immunity to experimental murine salmonellosis caused by an avirulent strain of Salmonella typhimurium, SL3235. Specifically this work hopes to accomplish the following: 1. To determine if the route of immunization will affect the specificity and/or magnitude of the T cell response. Mesenteric or inguinal and para-aortic lymph node T cells harvested from C3HeB/FeJ mice immunized with live SL3235 either per os or subcutaneously at the tail root, will be screened for antigen specificity by an in vitro proliferation assay. 2. Determine the surface phenotype of Salmonella specific lymph node T cells by immunofluorescence microscopy and flow cytometry. 3. To determine the effect of in vivo depletion of L3T4 + and Lyt2+ T cells on the ability of SL3235-immune C3HeB/FeJ mice to withstand virulent Salmonella challenge. This will be accomplished by intravenous administration of appropriate anti-T cell marker monoclonal antibodies. 4. Determine the capacity of lymph node T cells harvested from SL3235-immune mice to passively transfer protection, against virulent Salmonella challenge, to naive C3HeB/FeJ mice.